优化sed / tr shell脚本

Question

I wrote a script to automatically add a ServerAlias to an Apache configuration file, then restart Apache, with a rather remedial understanding of sed and tr and probably shell scripting in general. This is what I came up with:

cp /etc/httpd/sites/site.conf tmphost &&
sed s/ServerName\ site.com/ServerName\ site.com^#ServerAlias\ sub.site.com/ \
        tmphost |
    tr '^#' '\n\t' >/etc/httpd/sites/site.conf &&
rm -f tmphost &&
apachectl restart

Basically I'm creating a copy, replacing the ServerName line with itself + the new alias, using tr to put in the newline and tab ( sed was being weird about that?), overwriting the old configuration file, deleting the copy, then restarting Apache.

It works, but doesn't really make mama proud, if you know what I mean. Any ideas on how to clean that up?

Answer 1

If you want to add a ServerAlias line after ServerName line, why not use the 'append' command to add a line:

sed '/ServerName site.com/a\
    ServerAlias sub.site.com' tmphost >/etc/httpd/sites/site.conf

There's a 'tab' at the start of the extra line, which you seem to need.

If you have GNU sed, you can do the edit in-place with the -i option and without the temporary file (but don't use the -i option if the file you are editing has multiple hard links, and probably not it if it is a symlink, either; see the comments below from William Pursell ).

Note that you should wrap the code in:

trap "rm -f tmphost; exit 1" 0 1 2 3 13 15
...script manipulating tmphost...
rm -f tmphost
trap 0

so that the temporary file is not left around if the shell exits because of a signal. Of course, if you have an in-place alter, you don't need the temporary file at all.

Answer 2

I like the way with direct ServerAilas addition using sed :

sed -i "0,/^ServerName.\+/s//\0\nServerAlias sub.site.com/" /etc/httpd/sites/site.conf
apachectl reload